The present invention relates generally to hydrostatic pumps and motors and, more specifically, to ball and piston hydrostatic pumps and motors.
Hydrostatic pumps and motors are increasingly being used in the transfer of power due to their input/output flexibility, infinitely variable control and inherent overload protection. One such power transmission device is the bent-axis piston pump or motor, wherein the motor or pump includes parallel axis cylinders having pistons reciprocating therein.
Another power transmission device is the radial pump or motor One example of a radial pump or motor is the hydrostatic transmission disclosed by Simmons, U.S. Pat. No. 3,274,946. Because of the inherent high fluid pressures generated by hydrostatic pumps or motors, improvements thereto have generally focused on hydrostatically balancing resultant reaction loads so as to minimize size and complexity of the motor, while still providing maximum torque transmission.
For example, Ifield, U.S. Pat. No. 3,791,703, discloses a journal support bearing for rotating shafts, in which the journal support bearing includes a hydrostatically balanced slipper positioned within a stationary housing.
Most axial piston motors develop torque via side thrust loads transmitted across a ball joint at the the end of the pistons, wherein the side thrust loads are converted to torque by a disk articulatably rotating about its central axis. The long piston seals common to axial piston motors tend to limit leakage thereacross; however, at high loads and speeds the pistons in larger size motors can become sufficiently hot so as to seize within the cylinders. Also, at high rotating speeds sudden changes in loading can lift the rotor off the valve seat due to the high centrifugal loads, resulting in loss of drive.
Bent axis designs tend to reduce the piston side torque loads. However, double end ball push rods and large capacity thrust bearings and support structure are required for the variable reversible type motors. Furthermore, unbalanced high working fluid pressures can distort the cylinder housing and increase friction and heat build-up in the pistons.
Radial type pumps and motors include rotors which cannot lift off the pintle valve seat. Rather than having long stroke cylinders and pistons which substantially increase frictional losses with speed, the ball piston pump is a compact, high strength design employing large diameter cylinders with ball pistons having short strokes to increase capacity. For example, the stroke of the ball piston must be less than the ball radius. Also, the diametral clearance between the ball and cylinder is minimized to limit leakage. Still, CARBOLOY.RTM. cylinder liners, or other heat resistant liners, have been required to withstand the high temperatures caused by high torque loads occurring at high speeds. As a result, commercial radial units have fallen out of favor due to their cost and weight.
Therefore, there is a need for further improvements which reduce misalignment, leakage, cost and undesirable side torque loads and their associated frictional losses in a hydrostatic pump or motor. An improved hydrostatic pump/motor is desired which further balances fluid pressure loads therein. Such a fluid transmission device would be a radial hydrostatic pump/motor, in which loads are better distributed to reduce point contact loading and its resulting wear. Such a pump/motor would also include improved mechanical interfaces, wherein wear and slippage are further reduced. Such a pump/motor would be suitable for high speed motor vehicle propulsion and might find application in the bell housing of a Hydrocycle engine.